U.S. patent application number 10/043739 was filed with the patent office on 2002-07-11 for magnetic head actuator having finely movable tracking device.
This patent application is currently assigned to Alps Electric Co., Ltd.. Invention is credited to Abe, Hideki, Nagao, Koji, Nakagawa, Masayoshi, Nakazawa, Tohru.
Application Number | 20020089793 10/043739 |
Document ID | / |
Family ID | 18872156 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020089793 |
Kind Code |
A1 |
Nakagawa, Masayoshi ; et
al. |
July 11, 2002 |
Magnetic head actuator having finely movable tracking device
Abstract
A magnetic head actuator provided with a finely movable tracking
device having a piezoelectric element is provided for easy wiring
to the piezoelectric element and reducing problems such as wire
breakage and continuity defects. In the magnetic head actuator, a
portion of an FPC board resin base is removed to expose a portion
of the feeding line that extends onto a voltage impressing
electrode. An electrical and mechanical connection is made between
the electrode and the exposed portion of the feeding line by
ultrasonic bonding, Au ball bonding, or stud bumping.
Inventors: |
Nakagawa, Masayoshi;
(Niigata-ken, JP) ; Nakazawa, Tohru; (Niigata-ken,
JP) ; Abe, Hideki; (Niigata-ken, JP) ; Nagao,
Koji; (Niigata-ken, JP) |
Correspondence
Address: |
Brinks Hofer Gilson & Lione
P.O. Box 10395
Chicago
IL
60610
US
|
Assignee: |
Alps Electric Co., Ltd.
|
Family ID: |
18872156 |
Appl. No.: |
10/043739 |
Filed: |
January 9, 2002 |
Current U.S.
Class: |
360/294.4 ;
G9B/5.193; G9B/5.194 |
Current CPC
Class: |
G11B 5/5552 20130101;
H05K 2201/10083 20130101; H05K 2201/0397 20130101; H05K 2201/0969
20130101; H05K 2201/0394 20130101; G11B 5/4873 20130101; H05K 1/189
20130101; H05K 2203/0285 20130101; H05K 3/328 20130101; H05K
2201/10234 20130101; G11B 5/5556 20130101 |
Class at
Publication: |
360/294.4 |
International
Class: |
G11B 005/56 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2001 |
JP |
2001-003882 |
Claims
What is claimed is:
1. A magnetic head actuator having a finely movable tracking device
comprising: a swing arm having a magnetic head at a free end and
reciprocally movable around a coarse rotation axis at a base of the
swing arm; a piezoelectric element mounted in the swing arm, the
piezoelectric element having a voltage-impressing electrode for
allowing a fine arcuate movement of the free end around the coarse
rotation axis in response to an applied voltage; an FPC board
having a resin base and a feeding line embedded in the resin base
for feeding power to the voltage-impressing electrode, wherein a
portion of the resin base is removed to expose a portion of the
feeding line that extends onto the electrode; and an electrical
connection between the feeding line and the voltage impressing
electrode at the exposed portion of the feeding line.
2. The magnetic head actuator according to claim 1, wherein the
electrical connection comprises an ultrasonic bond.
3. The magnetic head actuator according to claim 1, wherein the
electrical connection comprises an Au ball bond.
4. The magnetic head actuator according to claim 1, wherein the
electrical connection comprises a through-hole in the exposed
portion of feeding line that is electrically connected to the
voltage-impressing electrode by a gold ball positioned in the
through-hole.
5. The magnetic head actuator according to claim 1, wherein the
electrical connection comprises a stud bump made of conductive
material residing on the piezoelectric element, and wherein the
exposed portion of the feeding line is electrically connected to
the voltage-impressing electrode by a stud bump positioned in a
through-hole located in the exposed portion of the feeding
line.
6. The magnetic head actuator according to claim 1 further
comprising a pair of piezoelectric elements having polarities
opposite to each other.
7. The magnetic head actuator according to claim 1, further
comprising a trace line leading to the magnetic head and extending,
together with the feeding line, in the FPC board.
8. A magnetic head actuator having a finely movable tracking
device, comprising: a swing arm having a magnetic head at a free
end and reciprocally movable around a coarse rotation axis of a
base of the swing arm; a piezoelectric element mounted in the swing
arm, the piezoelectric element having a voltage-impressing
electrode for allowing a fine arcuate movement of the free end
around the coarse rotation axis when a voltage is applied; and an
FPC board having a resin base and a feeding line embedded in the
resin base for feeding power to the voltage-impressing electrode,
wherein the feeding line resides completely within the FPC board
except for an exposed portion to extending onto the
voltage-impressing electrode, and wherein the exposed portion is
bonded to the piezoelectric element, by a direct electrical
connection between the voltage-impressing electrode and the exposed
portion.
9. The magnetic head actuator according to claim 8, wherein the
direct electrical connection comprises an ultrasonic bond.
10. The magnetic head actuator according to claim 8, wherein the
direct electrical connection comprises an Au ball bond.
11. The magnetic head actuator according to claim 8, wherein the
electrical connection comprises a through-hole in the exposed
portion of the feeding line that is electrically connected to the
voltage-impressing electrode by a gold ball positioned in the
through-hole.
12. The magnetic head actuator according to claim 8, wherein the
electrical connection comprises a stud bump made of a conductive
material residing on the piezoelectric element, and wherein the
exposed portion of the feeding line is electrically connected to
the voltage-impressing electrode by a stud bump positioned in a
through-hole located in the exposed portion of the feeding
line.
13. The magnetic head actuator according to claim 8 further
comprising a pair of piezoelectric elements having polarities
opposite to each other.
14. The magnetic head actuator according to claim 8, further
comprising a trace line leading to the magnetic head and extending,
together with the feeding line, in the FPC board.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a magnetic head actuator
having a finely movable tracking device and, more particularly, to
a power feeding structure for wiring to a piezoelectric element of
the tracking device.
[0003] 2. Description of the Related Art
[0004] A magnetic head actuator widely used in an HDD is provided
with a magnetic head opposing a rotating hard disk. The magnetic
head is positioned at the free end of a swing arm, which swings
reciprocally around the rotation axis of the base of the swing arm.
In accordance with tracking signals from the hard disk, the
actuator allows the swing arm to swing around the rotation axis. In
order to meet the demand for a narrower track width or a smaller
track pitch, a finely movable tracking device is constructed, such
that a piezoelectric element, which expands and contracts when a
voltage is applied, is mounted in the swing arm. Thus, the free end
of the swing arm makes a fine arcuate movement around the rotation
axis of the arm in accordance with expansion and contraction of the
piezoelectric element.
[0005] In a conventional magnetic head actuator provided with the
finely movable tracking device, a ground electrode of the
piezoelectric element is electrically connected to the swing arm,
and power is supplied to a voltage-impressing electrode via a
feeding line of a flexible printed circuit (FPC) board that extends
along the swing arm. The feeding line of the FPC board and the
voltage-impressing electrode of the piezoelectric element are
bonded by conventional gold (Au) wire bonding.
[0006] The Au wire bonding, however, is not only expensive due to
the many man-hours required but also the Au wire bond is easily
broken by an external force applied to the thin Au wire, which has
a diameter on the order of a few micrometers. Also, a component,
such as a magnetic head actuator that is incorporated into an HDD
in an additional step after assembly the wiring is easily broken,
thereby leading to continuity defects and low yield.
SUMMARY OF THE INVENTION
[0007] The present invention provides a magnetic head actuator with
a finely movable tracking device that which facilitates wiring to a
piezoelectric element, while reducing problems such as wire
breakage and continuity defects in the wiring.
[0008] The present invention facilitates connecting a
voltage-impressing electrode of a piezoelectric element and a
feeding line of an FPC board without using Au wire bonding. To this
end, the feeding line of the FPC board is arranged to extend onto
the voltage-impressing electrode, where an exposed portion is
formed by removing a resin base of the FPC board that extends onto
the electrode. Also, an electrical and mechanical connection to the
electrode at the exposed portion is made by ultrasonic bonding, Au
ball bonding or stud bumping.
[0009] A magnetic head actuator having a finely movable tracking
device according to the present invention comprises a swing arm
having a magnetic head at the free end of the swing arm, the swing
arm being reciprocally movable around a coarse rotation axis of the
base of the swing arm; a piezoelectric element, mounted in the
swing arm, for allowing a fine arcuate movement of the free end
around the coarse rotation axis when a voltage is applied; and an
FPC board having a resin base and a feeding line embedded in the
resin base for feeding power to a voltage-impressing electrode. The
feeding line of the FPC board is arranged to extend onto the
voltage-impressing electrode of the piezoelectric element. The
feeding line has an exposed portion formed by removing the resin
base from a portion of the feeding line extending onto the
electrode and a direct electrical connection is made to the
electrode at the exposed portion.
[0010] In another aspect of the present invention, in the magnetic
head actuator, the feeding line of the FPC board is arranged to
extend onto the voltage-impressing electrode of the piezoelectric
element. The feeding line lies in the FPC board other than the
portion to be bonded to the piezoelectric element. A direct
electrical connection is made to the electrode at the exposed
portion of the feeding line.
[0011] Specifically, as used herein, electrical conduction means
any mechanical and electrical bonding, and may include ultrasonic
bonding, Au ball bonding, and the like.
[0012] Preferably, the feeding line arranged to extend onto the
voltage-impressing electrode of the piezoelectric element is
partially exposed at the upper and lower portions of the feeding
line. After a through-hole is formed at the exposed portion, a gold
ball is inserted into the through-hole and the feeding line is
electrically bonded to the electrode by gold ball bonding.
Alternatively, after forming a stud bump made of conductive
material on the piezoelectric element, the feeding line is
electrically connected to the electrode by inserting the stud bump
into the through-hole of the feeding line.
[0013] Although a swing arm can provide a single piezoelectric
element in a preferred embodiment of the invention, the swing arm
is provided with a pair of piezoelectric elements having polarities
opposite to each other so that the magnetic head makes a larger
movement.
[0014] Although an FPC board having a feeding line leading to the
piezoelectric element can be prepared separately, in a preferred
embodiment the FPC board includes a trace line leading to the
magnetic head and extending in the FPC board.
[0015] Thus, the present invention provides a magnetic head
actuator, provided with a finely movable tracking device using a
piezoelectric element that facilitates wiring to the piezoelectric
element while reducing problems such as wire breakage and
continuity defects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a plan view of an HDD provided with a magnetic
head actuator according to the present invention;
[0017] FIG. 2 is a rear view of the sole magnetic head actuator
(swing arm) shown in FIG. 1;
[0018] FIG. 3 is a cross-sectional view taken along the lines
III-III shown in FIG. 2;
[0019] FIG. 4 is an enlarged plan view of a portion of the magnetic
head actuator according to a first embodiment of the present
invention;
[0020] FIG. 5 is a cross-sectional view taken along the line V-V
shown in FIG. 4;
[0021] FIG. 6 is a cross-sectional view taken along the lines VI-VI
shown in FIG. 4;
[0022] FIG. 7 is a cross-sectional view taken along the lines
VII-VII shown in FIG. 4;
[0023] FIG. 8 is a schematic view illustrating the bonding
structure of a feeding line of an FPC board and a
voltage-impressing electrode of a piezoelectric element according
to the first embodiment;
[0024] FIG. 9 is a partial cross-sectional view of the bonding
state in FIG. 8;
[0025] FIG. 10 is a schematic view illustrating the bonding
structure of a feeding line of the FPC board and the
voltage-impressing electrode of the piezoelectric element according
to a second embodiment of the present invention;
[0026] FIG. 11 is a schematic view illustrating a bonding state
after the bonding in FIG. 10 is completed;
[0027] FIG. 12 is a partial cross-sectional view illustrating the
bonding state shown in FIG. 11;
[0028] FIG. 13 is an enlarged plan view of a portion of the
magnetic head actuator according to a third embodiment of the
present invention;
[0029] FIG. 14 is an enlarged plan view of a feed line portion in
accordance with the third embodiment where feeding line is exposed
by removing a resin base of the FPC board;
[0030] FIG. 15 is a schematic view illustrating the bonding
structure of the feeding line of the FPC board and the
voltage-impressing electrode of the piezoelectric element according
to a third embodiment of the present invention;
[0031] FIG. 16 is a cross-sectional view illustrating a bonding
structure in accordance with the third embodiment before the
bonding in FIG. 15 is performed;
[0032] FIG. 17 is a cross-sectional view illustrating the bonding
structure in accordance with the third embodiment after the bonding
in FIG. 15 is completed;
[0033] FIG. 18 is a schematic view illustrating the bonding
structure of the feeding line of the FPC board and the
voltage-impressing electrode of the piezoelectric element according
to a fourth embodiment of the present invention;
[0034] FIG. 19 is a cross-sectional view illustrating the bonding
structure according to the fourth embodiment in which the bonding
in FIG. 18 is in progress; and
[0035] FIG. 20 is a cross-sectional view illustrating the bonding
structure according to the fourth embodiment after the bonding in
FIG. 18 is completed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] FIG. 1 shows an overall structure of an HDD provided with a
magnetic head actuator according to embodiments of the present
invention. Away from a hard disk (magnetic disk) 12 rotating along
a rotation axis 11, the base of a swing arm 20 comprising a load
beam and a gimbal spring is supported in a reciprocally swinging
manner around a coarse rotation axis 13. A magnetic head (flexure)
21 is supported at the free end of the swing arm 20. The magnetic
head 21 moves reciprocally in the substantially radial direction of
the hard disk 12 when the swing arm 20 is swung reciprocally around
the coarse rotation axis 13 by an actuator 14.
[0037] A pair of piezoelectric elements 22 having polarities
opposite to each other are mounted in parallel in the swing arm 20
on both sides of an imaginary line drawn between the coarse
rotation axis 13 and the magnetic head 21. As shown in FIGS. 1 and
3, the piezoelectric elements 22 each have a ground electrode 22G
on one of the front and back surfaces thereof and a
voltage-impressing electrode 22V on the other surface. The
piezoelectric elements 22 are polarized, such that long sides L of
the piezoelectric elements 22 are parallel to the imaginary line,
and one of the long sides L expands while the other contracts when
the same voltage is placed across the ground electrode 22G and the
voltage-impressing electrode 22V of each piezoelectric element
22.
[0038] In order to transmit expansion and contraction in the
direction of the long side L of the pair of piezoelectric elements
22 to the swing arm 20, the swing arm 20 has a pair of spaces 20S
therein for accommodating the piezoelectric elements 22. Each
piezoelectric element 22 has clearances on both ends in the
direction of the long side L as shown in FIG. 3. The clearances are
filled with an insulating non-shrinkable resin 24. The pair of
piezoelectric elements 22 mounted in the swing arm 20, as described
above, allow a fine arcuate movement of the magnetic head 21 of the
swing arm 20 around the coarse rotation axis 13 when one of the
piezoelectric elements 22 expands, while the other contracts. When
one of the piezoelectric elements 22 expands while the other
contracts by, for example, about 1 .mu.m, the current technology
level permits the magnetic head 21 to make a fine movement of about
10 .mu.m in the arcuate direction around the coarse rotation axis
13. In this embodiment, the swing arm 20 is grounded through
electrical connection with the ground electrodes 22G via an
electrically conductive resin 25 made of metal or conductive
material as shown in FIG. 3.
[0039] As illustrated in FIG. 2, commonly used for the magnetic
head 21 and the piezoelectric elements 22, has trace lines 32
leading to the magnetic head 21 and a pair of feeding lines 33
leading to the corresponding piezoelectric elements 22. These lines
32 and 33 are both embedded in a resin base 31 (shown, for example,
in FIGS. 4 and 5), which is typically formed of a polyamide resin.
The trace lines 32 are connected to the magnetic head 21 at one end
of the trace lines 32 and to a record-playback circuit 15 at the
other end. The feeding lines 33 are connected to the corresponding
voltage-impressing electrodes 22V of the piezoelectric elements 22
at one end of the feeding lines 33. The feeding lines 33 are also
connected to a control circuit 16 at the other end thereof.
Referring back to FIG. 1, the control circuit 16 is connected to
the actuator 14. The actuator 14 and the piezoelectric elements 22
are controlled in accordance with control signals transmitted from
the control circuit 16. The magnetic head 21 sends tracking signals
received from the hard disk 12 to the control circuit 16, while
exchanging record-playback information signals with the
record-playback circuit 15. With this configuration, the control
circuit 16 allows the swing arm 20, i.e., the magnetic head 21
controls the actuator 14 and the piezoelectric elements 22 so as to
move in a proper track position.
[0040] In the above configuration, the embodiment has structural
features for connecting the piezoelectric elements 22 of the
magnetic head actuator and the corresponding feeding lines 33. As
described previously, the piezoelectric element 22 and the feeding
line 33 have been bonded by known Au wire bonding, thereby causing
problems of high cost and wire breakage.
[0041] In the following description with respect to bonding between
the feeding lines 33 and the corresponding voltage-impressing
electrodes 22V, a combination of the feeding line 33 and the
corresponding voltage-impressing electrode 22V will be referred to,
since the other combination is bonded in the same manner.
[0042] FIGS. 4 to 9 illustrate a first embodiment of the present
invention. The FPC board 30, having the resin base 31 and the
feeding lines 33, is arranged to extend onto the voltage-impressing
electrodes 22V of the piezoelectric elements 22. The feeding lines
33 are partially exposed by removing the resin base 31 from the
portion of feeding lines 33 that extend onto the voltage-impressing
electrodes 22V. The feeding lines 33 are typically composed of
copper (Cu) and have gold plating layers 34 on the exposed portions
of the front and back surfaces of the feeding lines 33. The resin
base 31 and the feeding lines 33 both extend onto the
voltage-impressing electrodes 22V and are held on the side of the
FPC board 30 until the feeding line 33 is connected to the
piezoelectric element 22. The feeding lines 33 have a thickness of,
for example, about 10 to about 20 .mu.m.
[0043] In this embodiment, the feeding line 33 of the FPC board 30
abuts against the voltage-impressing electrode 22V, and an
ultrasonic probe 41 is brought into contact with the portion of the
feeding line 33 lying on the voltage-impressing electrode 22V.
Then, the feeding line 33 and the voltage-impressing electrode 22V
are bonded by ultrasonic bonding. During the ultrasonic bonding
process, the gold in the gold plating layers 34 on the front and
back surfaces of the feeding line 33 is dispersed into the surface
layer of the voltage-impressing electrode 22V, thereby bonding the
feeding line 33 and the electrode 22V.
[0044] FIGS. 10 to 12 illustrate a second embodiment of the
invention, in which the feeding line 33 and the voltage-impressing
electrode 22V are bonded with a gold ball 42 by well-known Au ball
bonding instead of the ultrasonic bonding. The bonding according to
the second embodiment can cause less damage to the feeding lines 33
than bonding, thereby potentially providing more reliable
connections.
[0045] FIGS. 13 to 17 illustrate a third embodiment of the present
invention. The feeding line 33, embedded in the resin base 31 of
the FPC board 30, is partially exposed at the upper and lower
portions of the feeding line 33 that extend onto the
voltage-impressing electrode 22V of the piezoelectric element 22.
In this embodiment, the resin base 31 at the end of the feeding
line 33 is partially removed in a round form so as to leave a
remaining ring 31A on the front and back surfaces of the feeding
line 33. The resin removed portion is thereby surrounded by the
remaining ring 31A. The resin base 31, typically formed of a
polyamide resin, covers and reinforces the feeding line 33 other
than the inside of the remaining ring 31A. In this configuration,
the feeding line 33 is rarely broken without exerting an external
force. The feeding line 33 has a through-hole 33A inside the
remaining ring 31A. A remaining portion is not necessarily
circular; however, it is advantageous from the viewpoint of
strength that the remaining portion is formed in a closed loop. The
inner diameter of the remaining ring 31A is, for example, about 0.2
to about 0.7 mm.
[0046] In this embodiment, the remaining ring 31A is placed on the
voltage-impressing electrode 22V and a gold ball 43 is inserted
through the through-hole 33A toward the voltage-impressing
electrode 22V. Then, the feeding line 33 of the FPC board 30 and
the voltage-impressing electrode 22V are bonded by Au ball bonding.
The bonding according to this embodiment, the remaining ring 31A of
the resin base 31, reinforces the feeding line 33. Accordingly,
there are few possibilities for wire breakage and the
manufacturability and reliability of the magnetic head actuator are
also improved.
[0047] FIGS. 18 and 19 illustrate a fourth embodiment of the
invention, bonding the feeding line 33 and the voltage-impressing
electrode 22V is completed by stud bumping instead of Au ball
bonding. The voltage-impressing electrode 22V has a stud bump 45
thereon that is accreted in advance of bonding by discharging a
gold ball. The stud bump 45 consists of a large diameter portion
45a firmly bonded to the voltage-impressing electrode 22V, and a
small diameter portion 45b formed on the large diameter portion
45a. The shape of the stud bump 45 is determined depending on the
shape of a capillary for a gold ball.
[0048] The feeding line 33 of the FPC board 30 and the
voltage-impressing electrode 22V are bonded as follows. After the
small diameter portion 45b of the stud bump 45 is inserted into the
through-hole 33A of the feeding line 33, an ultrasonic probe is
brought into contact on the small diameter portion 45b so as to
crush the small diameter portion 45b. In accordance with this
embodiment of the invention, a sufficient area is provided for
bonding the feeding line 33 and the voltage-impressing electrode
22V, thereby enhancing the reliability of the connection.
[0049] As illustrated in FIGS. 4 to 9, although the gold plating
layer 34 must be formed on the front and back surfaces of the
feeding line 33 for the ultrasonic bonding process used to
fabricate a magnetic head actuator according to the first
embodiment, the gold plating layer 34 is optional in the bonding
process used to fabricate a magnetic head according to the other
embodiments. The gold plating layer 34, however, has an advantage
in enhancing the electrical and mechanical bonding strength.
[0050] Technologies for forming the trace lines 32 and the feeding
lines 33 with an arbitrary pattern in the resin base 31 of the FPC
board 30 have already been established. Further, the resin base 31,
once formed, can also be easily patterned with an arbitrary pattern
by a physicochemical method, such as etching. Specifically, in a
reactive ion etching (RIE) device, for example, the resin base
reacts with gas ions to partially remove the resin base and thus
form a pattern.
* * * * *